<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>学习jQuery对象属性等</title>
</head>

<body>
    <ul>
        <li id="elem">第一个节点</li>
        <li>第二个节点</li>
        <li>第三个节点</li>
        <li>第四个节点</li>
    </ul>
</body>
<script src="../js/jquery.js"></script>
<script>
    console.log($("#elem"));
    console.log($("#elem").length);

    console.log($("ul li"));
    console.log($("ul li").length);

    console.log($("#elem2"));
    console.log($("#elem2").length);
</script>

</html>